1. Technical Field
The invention relates to a bitumen mixture for high-quality built-structure waterproofing systems, namely a bitumen mixture for an overlayment roofing membrane comprising at least distillation bitumen, SBS rubber and at least one filler.
2. Prior Art
Built-structure waterproofing systems comprising bitumen mixtures are used as roofing membranes, bridge waterproofing systems, basement envelopes and the like. Roofing membranes are used as roof waterproofing systems in the flat-roof sector in particular. Such roof water-proofing systems are generally made multilayered by disposing an overlayment roofing membrane on at least one underlayment roofing membrane. The overlayment roofing membrane, which is exposed to the elements and in particular high mechanical and thermal stresses, has to meet particularly high requirements. Therefore, overlayment roofing membranes, like other highly stressed built-structure waterproofing systems, are produced from high-quality bitumen mixtures. Such high-quality bitumen mixtures are based on polymer-modified bitumen. Polymer-modified bitumen is appreciably more costly than oxidic bitumen, used for example to produce roofing membranes which have to meet lower requirements, such as underlayment roofing membranes for example.
Both oxidic bitumen and polymer-modified bitumen are based on distillation bitumen. In the case of polymer-modified bitumen, distillation bitumen is modified with suitable polymeric materials of construction, such as SBS rubber or APP (atactic polypropylene), while in the case of oxidic bitumen the distillation bitumen is progressively oxidized at high temperatures of about 280° C. by addition of oxygen.
Distillation bitumen is inherently very soft and therefore cannot be used alone as bitumen material for high-quality built-structure waterproofing systems, in particular overlayment roofing membranes. To meet the requirements of high-quality built-structure waterproofing systems, the SBS rubber content has to be at least 10% by weight. Because SBS rubber is very costly, this greatly adds to the cost of the bitumen mixture.
Bitumen mixtures are admixed with fillers to reduce cost. The most common fillers are slate flour or limestone flour. Owing to the high viscosity, it is generally not possible to produce bitumen mixtures having a filler content of more than 30% by weight. This holds for high-quality built-structure waterproofing systems in particular.